PIRE: DUST stimulated drawn-down of atmospheric CO2 as a trigger for Northern Hemisphere Glaciation

了解过去5000万年来长期全球变冷背后的地质过程对于理解当今地球的气候条件很重要。北半球在4MYR以前基本上是无冰的，随后全球气温在约3.6MYR之前加速下降，北半球大陆的冰盖在约2.7MYR之前形成。有限的大气二氧化碳记录表明，在这段时间内，二氧化碳从百万分之400下降到百万分之300，可能已经足够冷却地球，使冰盖得以生长。然而，二氧化碳减少的原因仍不清楚。这项由7个美国机构和3个中国机构开展的国际研究和教育合作将评估一个新的假设：来自中亚沙漠的大气粉尘使北太平洋肥沃，刺激藻类生产力，进而减少大气中的二氧化碳，导致北半球冰川(NHG)。通过中国的野外工作研究，海洋和陆地沉积的实验室分析，以及大气和海洋模型研究，研究人员和学生将生成并比较来自不同地质档案的广泛的古气候记录，以评估大气尘埃在NHG开始时二氧化碳下降和全球变冷中的作用。这项研究项目的发现最终可能有助于提供具有全球政策含义的知识。通过评估大气尘埃在维持地球凉爽气候条件方面的重要性，这项研究有望阐明最近地质历史中气候变冷的机制。具体地说，这项研究将建立以下记录：1)中亚、藏北和中国黄土高原(CLP)的干旱化历史，与这些地区及其以西的亚洲高压地区的变形和地表抬升记录有关；2)中亚盆地的风蚀和CLP中的沙尘积累；3)北太平洋和南大西洋的沙尘通量、藻类生产力和海面温度；4)4.5-2.5 Ma的陆地CO2。模拟和敏感性研究将：(1)评估亚洲气候和尘埃循环对地形增长和背景全球气候的敏感性；(2)确定上新世尘埃输送到北太平洋可能导致的冷却量；(3)评估亚洲尘埃对大气二氧化碳的潜在影响。通过这个研究项目，美国研究生将有机会接触到中国的研究设施以及原本无法进入的野外地点，并通过双边访问与中国合作伙伴开展互利合作研究活动；美国本科生还将有机会参加暑期学校、研讨会和研究项目；调查人员将为博物馆开发外联工具，以增加公众对大气沙尘在气候变化中的作用的了解。

Understanding the geologic processes underlying the long-term global cooling over the past 50 million years (myr) is important for understanding the climate conditions on Earth today. The Northern Hemisphere was largely ice-free 4 myr ago followed by an acceleration of global temperature decline at ~3.6 myr ago, with continental ice sheets developing on northern hemisphere continents by ~2.7 myr ago. Limited atmospheric CO2 records suggest a decline in CO2 from ~400 to ~300 parts per million by volume (ppmv) during that time period could have cooled the Earth sufficiently to enable ice sheets to grow. Yet the cause for this decline in CO2 remains unknown. This international research and educational collaboration between 7 U.S. and 3 Chinese institutions will evaluate a new hypothesis: atmospheric dust derived from Central Asian deserts fertilized the North Pacific ocean, stimulating algal productivity, which in turn drew down atmospheric CO2 leading to Northern Hemisphere Glaciation (NHG). Through field work studies in China, laboratory analyses of ocean and terrestrial sedimentary deposits, and atmospheric and ocean modeling studies, the investigators and students will generate and compare a wide range of paleoclimate records from diverse geological archives to evaluate the role of atmospheric dust in CO2 decline and global cooling at the onset of NHG. The findings from this research project may ultimately contribute to knowledge with global policy implications.By evaluating the significance of atmospheric dust in sustaining cool climate conditions on Earth, this study is expected to elucidate the mechanisms of climate cooling in the recent geologic past. Specifically this study will establish records of: 1) the aridification history of Central Asia, northern Tibet, and the Chinese Loess Plateau (CLP) as related to records of deformation and surface uplift in high Asia within and to the west of these regions, 2) wind erosion of Central Asia basins and dust accumulation in the CLP, 3) dust flux, algal productivity, and sea surface temperature in the North Pacific and South Atlantic, and 4) terrestrial CO2 in the interval of 4.5-2.5 Ma. Modeling and sensitivity studies will (1) evaluate the sensitivity of Asian climate and the dust cycle to the growth of topography and to the background global climate; (2) determine the amount of cooling that could result from Pliocene dust transport to the North Pacific; (3) evaluate the potential influence of Asian dust on atmospheric CO2. Through this research program, US graduate students will gain access to research facilities as well as field localities in China that would otherwise be inaccessible and engage in mutually beneficial collaborative research activities with Chinese partners via bilateral visits; US undergraduate students will also have the opportunity to participate in summer schools, workshops, and research projects; the investigators will develop outreach tools for museums to increase public understanding of the role of atmospheric dust in climate change.